Functions of the M-CSF receptor on osteoclasts

Macrophage colony-stimulating factor (M-CSF) receptor has been previously reported to be present in osteoclasts both at mRNA and protein levels. However, the biochemical interactions between M-CSF and its receptor on osteoclasts are less well characterized than in mononuclear phagocytes. In this study, we show that (1) 125I-labeled M-CSF ligand specifically binds to the M-CSF receptor on osteoclasts by autoradiography; (2) binding of M-CSF to the receptor stimulates protein tyrosine phosphorylation in osteoclasts by immunostaining; (3) oxygen-derived free radicals produced by calvarial osteoclasts are increased by M-CSF stimulation (1.37 +/- 0.08, n = 10, P < 0.01); and (4) bone resorption in calvarial explants is enhanced by M-CSF (1.153 +/- 0.09, n = 10, p < 0.001). Thus, our data provide multiple lines of evidences that mouse calvarial osteoclasts are activated by M-CSF. These data suggest that under the conditions present in the calvarial model, M-CSF activates osteoclastic bone resorption.